1. Field of the Invention
The present invention relates to a machine learning system and a magnetizer for a motor, and in particular relates to a machine learning system and a magnetizer for a motor having the function of determining a voltage command to flow an optimal current for obtaining a desired magnetization rate.
2. Description of Related Art
To magnetize permanent magnets, it is necessary to apply a magnetic field the strength of which reaches the saturation point of the maximum magnetic flux density of a magnetic material, and magnetization units are used therefor. The magnetization units include a magnetizing yoke and windings for generating magnetic fields to provide a magnetic material with magnetic properties. As an example of the magnetization unit, a capacitor discharge magnetization unit in which a capacitor is charged and energy accumulated in the capacitor is discharged into the magnetizing yoke to generate a strong magnetic field is known.
FIG. 1 shows an example of a circuit of a conventional magnetization unit (for example, Japanese Unexamined Patent Publication (Kokai) No. 2006-173447). The conventional magnetization unit includes a phase control circuit 1001 for controlling the phase of an alternating voltage, a step-up transformer 1002 for multiplying the voltage, a rectifier circuit 1003 for rectifying the multiplied voltage, a capacitor C1 to be charged with the rectified voltage, a switching element SCR1 for magnetization connected in parallel with the capacitor C1, and a magnetizing winding L1. In the conventional magnetization unit, upon the conduction of the SCR1 by an ignition pulse, a magnetizing current is supplied to the magnetizing winding L1. As a result of a back electromotive force generated in the magnetizing winding L1 from the time of the charged voltage of the capacitor C1 reaching zero, a circulating current flows through a flywheel diode D1. The circulating current of the flywheel diode D1 prevents heat generation in the winding, and regenerates the back electromotive energy.
When magnetizing a rotor made of a magnetic material in the conventional magnetization unit, a current flows at a constant voltage. However, in the case of magnetizing many rotors in a continuous manner, a copper wire constituting the magnetizing winding of the magnetization unit will gradually increase in temperature and hence increase in resistance, thus causing a reduction in the current flowing through the magnetizing winding. As a result, the magnetization rate of the rotors is reduced, so that a high magnetization rate cannot be maintained. Furthermore, the reduction in the magnetization rate of the rotor brings about a reduction in the torque of a motor.